We will be celebrating the life of the Reverend Dr. Martin Luther King, Jr. this Monday. This is also a time when many people stop to celebrate the accomplishments of African-Americans as a group. So NPR's Shankar Vendantam did a double take when he came by some counterintuitive new research into how feelings toward some African-Americans change on MLK Day. Shankar joins us regularly on the program to talk about social science research. He's back with us now. Hey, Shankar.

SHANKAR VEDANTAM, BYLINE: Good morning, David.

GREENE: So tell me about this double take you had.

VEDANTAM: Well, you know, like most people, David, I'd intuitively assumed that on MLK Day, most people would have an elevated view, not just of the Reverend Martin Luther King, Jr., but of African-Americans in general and prominent Americans in our midst, people like President Obama or former Secretary of State Colin Powell. I recently spoke with Sara Konrath at Indiana University. And she told me that she and her colleagues William Chopik, Ed O'Brien and Norbert Schwarz - they decided to test this intuitive belief that I thought many of us share. They had volunteers describe their feelings about African-Americans in general and a prominent African-American like Colin Powell. She told me that she was surprised by what she found.

SARA KONRATH: People see Powell in a negative light on MLK Day compared to how they see him on days that are before or after. But on MLK Day, people actually see African-Americans, as a group, more positively.

GREENE: OK, explain what's going on here. People see African-Americans in general more positively on this holiday. But someone like Colin Powell they see more negatively. Why does that happen?

VEDANTAM: On the service, David, it makes no sense. And initially, the researchers thought maybe this has something to do with Colin Powell. So they retested the experiment, and this time they used Barack Obama. And they found again the same thing, that people dislike the president more on MLK Day compared to other days. This wasn't just white people, by the way. This included African Americans. They found the same thing did not happen to prominent white leaders. So people such as Bill Clinton or Mitt Romney, for example, were not rated more negatively on MLK Day compared to other days.

GREENE: So things President Obama, Colin Powell have in common - I mean, political leaders, luminaries in the African-American community. Is that part of what's happening?

VEDANTAM: And I think that's exactly what's happening, David. The researchers think this might be less about racial bias and more about how our minds make judgments about other people. Konrath asked me to imagine another scenario. Imagine that there's a university professor who wins a Nobel Prize. She asked me to think how this would change my views of the department where the Nobel Prize winner works and my views of individual professors at the same department. Here she is again.

KONRATH: So as a whole, people are going to rate my department as, like, very good and very prestigious. But then, the individual faculty members, who are not Nobel Prize winners, suddenly look bad compared to that Nobel Prize winner.

GREENE: OK, so what she's saying is it's not like people are going to have a negative view of all researchers in the world. But she's being compared - she's seen as in the same category somehow as this Nobel Prize in her department. It's a matter of contrast, in a way.

VEDANTAM: That's exactly right, David. So people are rating Colin Powell and Barack Obama worse on MLK Day because they're unconsciously comparing these prominent African-Americans to the Reverend King. Now, everyone would look worse compared to Dr. King. The interesting thing is how our minds choose these contrasts. And our minds choose these contrasts very selectively. Reverend King was not just a prominent African-American. He was a prominent African-American political figure and a man. So are Colin Powell and Barack Obama. And that's why the volunteers are unconsciously reaching for this contrast. When the researchers analyzed people's feelings about prominent African-Americans who are not politicians - Oprah Winfrey or Will Smith, for example - they were not affected in the same way. They were not evaluated more negatively on MLK Day. So the interesting thing, David, here, is that sometimes, being close to a star allows us to bask in reflected glory. Sometimes, if the star has many of the same characteristics that we do, we can end up looking worse by contrast.

GREENE: Shankar, interesting stuff as always. And that might explain why I feel less well-received when I'm in the studio with you.

VEDANTAM: (Laughter). Thanks so much, David.

GREENE: Thanks, Shankar. That's Shankar Vedantam. He regularly joins us to talk about social science research on the program. And you can follow him on Twitter @HiddenBrain. And you can follow this program @nprgreene, @NPRinskeep and @MorningEdition. Transcript provided by NPR, Copyright NPR.